1. Field of the Invention
This invention relates to a sensor apparatus for detecting the presence of selected or target gases where a Quantum Ferroelectric (QFE) copolymer sensing element in a housing is bombarded with infrared energy, which element includes a selected QFE copolymer that provides an electrical output dependent upon the IR absorption bands of the gases to be detected.
2. Description of the Prior Art
In the past, before the advent of passive type gas detectors, industrial safety and processing applications made use of robust and expensive electrochemical reactive type systems. The production of economical home safety sensors and commercial air handling apparatus for ventilation control has come to fruition due to the development of semiconductor and infrared sensitive ferroelectrics such as TriGlycine Sulfide and other crystalline materials. These materials are used as a component of the sensing element in apparatus which includes an outer can, a top mounted infrared filter to allow infrared energy only to pass through, and a sensing element, which contains materials that produce an electrical output when bombarded with infrared energy. This output is used to signal the presence of gas in the apparatus between the infrared source and the sensing element.
Crystalline ferroelectrics have become an industry standard sensor for use in Carbon Monoxide and Carbon Dioxide gas detection systems. Due to the hydroscopic nature of these crystalline sensing elements they are difficult to calibrate for the long term, have a short shelf life, with relative instability being the prime factor for potential liabilities, necessitating increased stocking and maintenance costs.
Some specific problems associated with a TGS Pyroelectric Detector are: Maximum operating temperature of 40° C. Responsivity progressively decreases at temperatures below 32° C., which is the optimum temperature (i.e., curie point of TGS). Maximum resolvable temperature differential of about 5° C. The need to repole the TGS crystal when its low Curie temperature is exceeded. TGS is hydroscopic and mechanically fragile. The operating lifetime of the TGS sensor crystal is about 2000 hours as a result of out gassing of the crystal, after prolonged exposure to infrared radiation.
The invention uses quantum ferroelectric copolymers (QFE) in place of the TriGlycine Sulfide (TGS) sensing element in traditionally accepted industry standard, non dispersing infrared (NDIR) gas sensors. Systems utilizing TGS as the sensing element are performance limited by the hydroscopic nature of the crystalline material. Atmospheric moisture, in gas form or condensation as encountered in commercial air handling systems, has a severe detrimental effect on the sensitivity and usable life cycle of the TGS infrared detector. QFE as a replacement for TGS as an NDIR sensing material operating at room temperature in the Pyroelectric mode, does not suffer from the prior art problems, and provides many advantages.